In recent years, large and small accidents among vehicles have occurred due to a rapid increase in the number of vehicles. Therefore, a forward collision warning system has been adopted in a lot of vehicles. A preceding vehicle that precedes a vehicle is close to its own vehicle due to momentary carelessness or drowsy driving of the driver, the forward collision warning system warns the driver.
In recent years, a technology has been under research, which notifies an emergency situation to the driver with respect to an opposite vehicle that comes closer from an opposite side to the vehicle in addition to the preceding vehicle.